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Effects of Light Intensity and Paclobutrazol on Growth and Interior Performance of Pachira aquatica Aubl.

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Pachira aquatica Aubl. has recently been introduced as an ornamental foliage plant and is widely used for interiorscaping. Its growth and use under low light conditions, however, have two problems: leaf abscission and accelerated internode elongation. This study was undertaken to determine if production light intensity and foliar application of paclobutrazol [beta-(4-chlorophenyl)methyl-alpha-(1,1-dimethylethyl)-1H- 1,2,4- triazole-1-ethanol] improved plant growth and subsequent interior performance. Two-year-old P. aquatica trunks were planted in 15-cm diameter plastic pots using a peat-based medium and were grown in a shaded greenhouse under three daily maximum photosynthetic photon flux densities (PPFD) of 285, 350, and 550 mu mol.m(-2).s(-1). Plant canopy heights, average widths, and internode lengths were recorded monthly over a 1-year production period. Two months after planting, the plant canopy was sprayed once with paclobutrazol solutions at concentrations of 0, 50, and 150 mg.L(-1), approximate to 15 mL per plant. Before the plants were placed indoors under a PPFD of 18 mu mol.m(-2).s(-1), for 6 months, net photosynthetic rates, quantum yield, and light saturation and compensation points were determined. Results showed that lowering production light levels did not significantly affect canopy height, width, or internode length but affected the photosynthetic light response curve and reduced the light compensation point. Foliar application of paclobutrazol reduced internode length, thereby resulting in plants with reduced canopy height and width and more compact growth form. Paclobutrazol application also reduced the light compensation point of plants grown under 550 mu mol.m(-2).s(-1). Plants with the compact growth form did not grow substantially, dropped fewer leaflets, and thus maintained their aesthetic appearance after placement indoors for 6 months. These results indicated that the ornamental value and interior performance of P. aquatica plants can be significantly improved by producing them under a PPFD range between 285 and 350 mu mol.m(-2).s(-1) and foliar spraying of paclobutrazol once at a concentration between 50 and 150 mg.L(-1).
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HORTSCIENCE 44(5):1291–1295. 2009.
Effects of Light Intensity and
Paclobutrazol on Growth and Interior
Performance of Pachira aquatica Aubl.
Qiansheng Li, Min Deng, Jianjun Chen
1
, and Richard J. Henny
University of Florida, IFAS, Department of Environmental Horticulture and
Mid-Florida Research and Education Center, 2725 Binion Road, Apopka, FL
32703
Additional index words. light acclimatization, light compensation point, money tree,
ornamental foliage plants
Abstract.Pachira aquatica Aubl. has recently been introduced as an ornamental foliage
plant and is widely used for interiorscaping. Its growth and use under low light
conditions, however, have two problems: leaf abscission and accelerated internode
elongation. This study was undertaken to determine if production light intensity and
foliar application of paclobutrazol [b-(4-chlorophenyl)methyl-a-(1,1-dimethylethyl)-
1H- 1,2,4- triazole-1-ethanol] improved plant growth and subsequent interior perfor-
mance. Two-year-old P.aquatica trunks were planted in 15-cm diameter plastic pots
using a peat-based medium and were grown in a shaded greenhouse under three daily
maximum photosynthetic photon flux densities (PPFD) of 285, 350, and 550 mmolm
2
s
1
.
Plant canopy heights, average widths, and internode lengths were recorded monthly over
a 1-year production period. Two months after planting, the plant canopy was sprayed
once with paclobutrazol solutions at concentrations of 0, 50, and 150 mgL
1
,
15 mL per
plant. Before the plants were placed indoors under a PPFD of 18 mmolm
2
s
1
for 6
months, net photosynthetic rates, quantum yield, and light saturation and compensation
points were determined. Results showed that lowering production light levels did not
significantly affect canopy height, width, or internode length but affected the photosyn-
thetic light response curve and reduced the light compensation point. Foliar application
of paclobutrazol reduced internode length, thereby resulting in plants with reduced
canopy height and width and more compact growth form. Paclobutrazol application also
reduced the light compensation point of plants grown under 550 mmolm
2
s
1
. Plants
with the compact growth form did not grow substantially, dropped fewer leaflets, and
thus maintained their aesthetic appearance after placement indoors for 6 months. These
results indicated that the ornamental value and interior performance of P.aquatica
plants can be significantly improved by producing them under a PPFD range between
285 and 350 mmolm
2
s
1
and foliar spraying of paclobutrazol once at a concentration
between 50 and 150 mgL
1
.
Pachira aquatica Aubl., a member of the
family Bombacaceae, is a tropical wetland
tree indigenous to Central and South America
from southern Mexico to Guyana and north-
eastern Brazil (Robyns, 1964). It has shiny
green palmate leaves with five to nine lance-
olate leaflets and a smooth green stem with a
distinctive swollen base. Flowers are showy
and have long, narrow petals and hair-like
yellowish orange stamens. In its native hab-
itat, P.aquatica grows under full sun or
partial shade and can reach 18 m in height.
Seeds are consumed raw (tastes like peanuts)
or as roasted beans with a flavor of chestnuts.
Thus, P.aquatica is also known as Malabar
chestnut or Guyana chestnut. Young leaves
and flowers are also edible as a vegetable
(Oliveira et al., 2000). Propagation of P.
aquatica is by means of seeds or stem
cuttings.
In addition to being a specialty food crop,
P.aquatica has recently been introduced as a
tropical ornamental foliage plant. Large
trunks are planted singly in containers or
small trees (four to six) are grown together
and braided as potted foliage plants used for
interiorscaping. Because of its swollen stem
base and flexibility of the branch and stem, P.
aquatica is also grown as bonsai or pseudo
bonsai. In East Asia, P.aquatica is known as
the money tree and is believed to bring
financial fortune in business. As an indoor
plant, P. aquatica has been shown to reduce
volatile organic compounds (Song et al.,
2007). The money tree is also becoming
popular in the United States as a potted house
plant or bonsai. However, there are two
common problems associated with its growth
and use under low light conditions, leaf
abscission and accelerated internode elonga-
tion, which are similar to the responses of
Ficus benjamina L. to low light levels (Chen
et al., 2001; Fonteno and McWilliams, 1978).
Thus far, there is no information available
regarding cultural practices to control the two
problems in P. aquatica.
Leaf abscission is a major factor influenc-
ing interior performance of many ornamental
plants (Embry and Northnagel, 1994). To
have a plant that is used to growing under
full sun or partial shade to better adapt to
interior low light environments, light accli-
matization is required (Chen et al., 2005a;
Conover and Poole, 1984). There are two
methods of light acclimatization (Chen et al.,
2005a). One is to grow plants under relatively
high light conditions to near-finished sizes
and then provide plants with a reduced light
level for 4 to 5 weeks or longer before
shipping to market for interiorscaping. The
other is to grow plants initially under reduced
light levels until marketable sizes are reached.
Light acclimatization improves the plant inte-
rior performance by lowering the light com-
pensation point, thus reducing leaf abscission
and maintaining the aesthetic values during
interiorscape (Chen et al., 2005a; Fonteno and
McWilliams, 1978; Reyes et al., 1996; Yeh
and Wang, 2000).
Production of plants under reduced light
levels, however, may modify some morpho-
logical traits such as increasing internode
length, which may affect the plant’s aesthetic
appearance, especially of some woody orna-
mental plants like Ficus and Schefflera
(Kubatsch et al., 2006). To reduce rapid
internode elongation under a low light level,
plant growth retardants have been used as a
foliar spray or soil drench (Davis, 1987).
Paclobutrazol [b-(4-chlorophenyl)methyl-a-
(1,1-dimethylethyl)-1H-1,2,4-triazole-1-eth-
anol] has been shown to control the height of
Caladium ·hortulanum Bird., Codiaeum var-
iegatum (L.) Blume, Schefflera actinophylla
Endl., Euphorbia pulcherrima Wind., and
Impatiens wallerana (L.) Hook. f. (Barrett
et al., 1994) as well as F. benjamina (Barrett
and Nell, 1983). Application of flurprimidol
{a–(methylethyl)-a-[4-(trifluoromethoxy)-
phenyl]-5-pyrimidinemethanol} or ancymi-
dol [a-cyclopropyl-a-(4-methoxyphenyl)-5-
pyrimidinemethanol] controlled the height
of Geogenanthus undatus C. Koch & Linden
(Burton et al., 2007). In a preliminary study
using different growth retardants, we found
that a foliar spray of paclobutrazol reduced
the internode elongation, thus controlling the
height of P. aquatica.
This study was undertaken to evaluate the
effects of light intensity and paclobutrazol
application on growth and subsequent inte-
rior performance of P. aquatica. The objec-
tive was to determine if the combination of
production light level and paclobutrazol
application could reduce the internode elon-
gation and leaf drop and improve P. aqua-
tica’s ornamental value as an indoor foliage
plant.
Materials and Methods
Two-year-old P.aquatica rooted trunks
(trunk diameter 3 to 4 cm and height 25 cm
Received for publication 17 Mar. 2009. Accepted
for publication 29 Apr. 2009.
We thank Penang Nursery, Inc., Apopka, FL, for
providing the Pachira aquatica plants used in this
study and Russell D. Caldwell for critical reading
of the manuscript.
1
To whom reprint requests should be addressed;
e-mail jjchen@ufl.edu.
HORTSCIENCE VOL. 44(5) AUGUST 2009 1291
with one branch) were obtained from a
commercial nursery in Apopka, FL, and
planted in 15-cm diameter plastic pots in
June 2006 using a sphagnum peat-based
medium (Vergro Container Mix A; Verlite
Co., Tampa, FL) in which Canadian peat,
vermiculite, and perlite were in a 3:1:1 ratio
based on volume. Potted plants were grown
in a shaded greenhouse under three daily
maximum photosynthetic photon flux densi-
ties (PPFD) of 285, 350, and 550
mmolm
–2
s
–1
, which resulted from the instal-
lation of shadecloth with three different
densities (Chen et al., 2005a). Temperatures
in the shaded greenhouse ranged from 20 to
32 C and relative humidity varied from 50%
to 100%. All plants were fertilized with top-
dress application of a 15N–7P
2
O
5
–15K
2
O
controlled-release fertilizer, Multicote, with
an 8-month longevity at a temperature of
21 C (Haifa Chemicals Ltd., Haifa Bay,
Israel) at a rate of 0.75 g nitrogen per pot.
Plants were irrigated three to four times a
week with a leaching fraction of 0.2. Two
months after planting, the plants had estab-
lished their canopies with five to six palmate
leaves. After recording canopy heights and
average widths (means of the widest width
and width perpendicular) and mean internode
length (stem height divided by the number of
nodes), plants grown under the three PPFD
were subjected to a one-time spray of paclo-
butrazol (Uniroyal Chemical Co., Middle-
bury, CT) solutions at rates of 0, 50, and 150
mgL
–1
of a.i., respectively. Approximately
15 mL of the solutions were sprayed per plant
with the potting medium surface covered to
keep paclobutrazol off the medium. The
experiment was arranged in a split plot design
with nine plants per treatment. Plants were
grown in the shaded greenhouse for an
additional 10 months, during which canopy
heights and average widths were measured
monthly. Mean internode lengths were
recorded at the end of production.
Photosynthetic light response curves were
measured in July 2007 using a Li-6400
portable photosynthesis meter (Li-COR Bio-
science, Lincoln, NE) on the newest devel-
oped mature leaves of each treatment. The
range of PPFD was set at 5, 15, 25, 50, 100,
250, 500, and 750 mmolm
–2
s
–1
using the Li-
6400-02B light source. The CO
2
concentra-
tion was set at 380 mmolmol
–1
, the rate of air
flow was maintained at 300 mmols
–1
, and the
leaf chamber (2 ·3 cm) temperature was set
at 28 C. Curve-fitting software (Sigma Plot
for Windows 10.0; Systat Software, Rich-
mond, CA.) was used to analyze the light
responses using a three-component exponen-
tial function equation A = a (1 – e
–bx
)+c
(Watling et al., 2000), where A = net photo-
synthetic rate and x = PPFD; a, b, and c were
parameters estimated by the nonlinear regres-
sion. Light-saturated photosynthesis rate A
sat
was calculated as a + c, and the quantum yield
of photosynthesis (A
qe
) was calculated as the
initial slope at A = 0 [calculated as b (a + c)].
The light compensation point was deter-
mined by solving this equation for PPFD at
Aof0mmolm
–2
s
–1
. The light saturation
point was determined by the PPFD at which
A was 99% of the light-saturated net photo-
synthesis (Burton et al., 2007; Peek and
Russek-Cohen, 2002; Watling et al., 2000).
To measure the anatomical characteris-
tics, recently matured leaves of plants pro-
duced from different treatments were taken in
July 2007 and fixed in FAA (formalin:glacial
acetic acid:70% ethanol at 5:5:90 by vol-
ume). After dehydration through an alcohol–
xylol series, the samples were embedded in
Paraplast with a 56 to 58 C melting point,
sectioned at 8 mm, and stained with Safranin-
Fast green and mounted on Permount (Fisher
Scientific, Inc., Pittsburgh, PA). Sections
were observed with a Nikon OPTIPHOT
microscope (Nikon Nippon Kogaku K.K.,
Tokyo, Japan) and photographed using a
Canon S3 IS digital camera (Cannon U.S.A.,
Inc., Lake Success, NY).
After photosynthesis measurement and
leaf anatomical examination, plants from five
replications were placed in interior evalua-
tion rooms with a PPFD of 18 mmolm
–2
s
–1
provided by white fluorescent lamps. All
interior rooms were lit 12 h daily with a
temperature set at 24 C and relative humid-
ity 50%. Plants were monitored weekly and
watered as needed for 6 months. The number
of dropped leaflets, plant height and width,
and mean internode length were recorded
monthly. The interior evaluation experiment
was arranged in a randomized block design.
There were five rooms as five blocks; each
room held nine plants, one per treatment.
Data were analyzed using the SAS Gen-
eral Linear Model procedure (SAS Institute,
1996). All data were subjected to analysis of
variance. When significant differences oc-
curred, means were separated by Duncan’s
new multiple range test at P= 0.05.
Results and Discussion
Effects on plant canopy. All plants ini-
tially had similar canopy heights (36.8 to 40.8
cm), average widths (48.2 cm to 52.9 cm),
and five to six palmate leaves before the foliar
spray of paclobutrazol. Canopy heights and
widths, internode lengths, and the percentage
of canopy height and width increases at the
end of production were not significantly dif-
ferent among plants grown under the three
light regimes without paclobutrazol treat-
ment (Table 1), althrough the net photosyn-
thetic rate of plants grown under 550
mmolm
–2
s
–1
was higher with A
max
of 4.7
compared with 4.2 and 3.3 at 350 and 285
mmolm
–2
s
–1
, respectively (Table 2). The
discrepancy between the higher net pho-
tosynthetic rate and nonsignificant increase
in the measured growth parameters could
be attributed to the higher photosynthesis-
enhancing plant dry matter accumulation
such as increased leaf thickness and mechan-
ical strength but not affecting plant form such
as canopy heights and widths. As shown in
Figure 1, the leaves of plants grown under
PPFD of 550 mmolm
–2
s
–1
were thicker than
those grown under 285 mmolm
–2
s
–1
.
Canopy height, internode length, and per-
centage of canopy height increase were sig-
nificantly reduced 10 months after the plants
Table 1. Effects of different light intensities and concentrations of paclobutrazol as a one-time foliar spray on Pachira aquatica plant growth in a shaded
greenhouse for 1 year.
Light intensity
(mmolm
–2
s
–1
)
Paclobutrazol concn
(mgL
–1
)
10 months after paclobutrazol application Mean internode
length (cm)
y
Percentage of increase
z
Canopy ht (cm) Canopy width (cm) Canopy ht Canopy width
285 0 81.4 a
x
92.7 a 10.7 a 95.7 a 78.3 ab
285 50 60.4 b 86.1 ab 1.2 b 50.2 b 62.8 abc
285 150 45.5 b 60.5 d 0.9 b 14.3 b 10.0 d
350 0 81.4 a 90.8 a 10.3 a 99.5 a 82.3 a
350 50 55.6 b 77.8 abc 0.9 b 36.9 b 44.9 abc
350 150 45.4 b 66.4 cd 0.8 b 15.8 b 26.5 d
550 0 82.8 a 87.4 ab 11.1 a 106.0 a 81.3 a
550 50 59.4 b 82.8 ab 1.1 b 50.8 b 71.8 abc
550 150 45.4 b 57.7 d 0.9 b 23.4 b 40.0 bcd
Significance
w
Light NS NS NS NS NS
Paclobutrazol ** ** ** ** **
Interaction NS NS NS NS NS
z
The percentage of canopy height or width increase was calculated as follows: (height or width at the end of production – height or width before paclobutrazol
application)/height or width before paclobutrazol application.
y
The mean internode length was the stem height divided by the number of nodes.
x
Means within column followed by different letters are significantly different by Duncan’s new multiple range test at P= 0.05.
w
NS indicates nonsignificant; **significant at P= 0.01 (n = 9).
1292 HORTSCIENCE VOL. 44(5) AUGUST 2009
were treated with paclobutrazol regardless of
the production light levels, but these param-
eters did not significantly differ between
plants treated with the two paclobutrazol
concentrations (Table 1). The average inter-
node lengths of plants treated with paclobu-
trazol ranged from 0.8 to 1.2 cm compared
with 10.3 to 11.1 cm of the control plants. As
a result, canopy heights increased only 14.3%
to 50.8% for plants treated with paclobutrazol
but 95.7% to 106.0% for control plants.
Canopy widths and percentages of canopy
width increase were significantly reduced by
paclobutrazol treatment at 150 mg/mL but not
at 50 mg/mL. Paclobutrazol application in
reduction of internode length was also
reported in Plectranthus australis R. Br.,
Zebrina pendula Schnizl., and F.benjamina
(Davis, 1987) as well as Gynura aurantiaca
(Blume) DC (Chen et al., 2002) and other
floriculture crops (Barrett et al., 1994). Paclo-
butrazol is an effective inhibitor that blocks
gibberellin biosysnthesis by inhibiting kaur-
ene oxidase, an enzyme-converting kaurene
to kaurenoic acid (Wang et al., 1986). When
gibberellin biosysnthesis is blocked, cell
division still occurs, but the new cells do
not elongate, which results in shoots with the
same numbers of leaves but compressed in-
ternodes (Chaney, 2003). As a consequence,
P.aquatica treated with paclobutrazol showed
a compact appearance, thereby increasing its
ornamental value.
Effects on photosynthesis. The net photo-
synthetic rates (A) of P.aquatica increased
rapidly as PPFD increased from 0 to 150
mmolm
–2
s
–1
and reached their saturation at a
PPFD range of 213 to 259 mmolm
–2
s
–1
(Fig.
2). In general, plants grown under higher
PPFD have high light saturation points
because of the higher level of enzymes for
carboxylation and electron transport (Callan
and Kennedy, 1995). In the present study,
light saturation points of plants grown under
the three PPFD regardless of paclobutrazol
treatments did not significantly differ except
for plants grown under 285 mmolm
–2
s
–1
and
treated by paclobutrazol at 150 mgL
–1
that
were significantly lower than plants grown
under 500 mmolm
–2
s
–1
without paclobutra-
zol treatment (Table 2). These results gen-
erally concurred with those reported by
Seemann (1989) in which light saturation
points of soybean (Glycine max L.) grown
under 250 to 500 mmolm
–2
s
–1
and 1000 to
1500 mmolm
–2
s
–1
were not significantly
different. The explanation was that plants
grown under 1000 to 1500 mmolm
–2
s
–1
had
higher Rubisco than those grown under 250
to 500 mmolm
–2
s
–1
. As a result, photosyn-
thesis per unit of Rubisco for plants grown
under the two light regimes were almost
equal and thus similar light saturation points
(Seemann, 1989).
The quantum yield (A
qe
) ranged from
0.033 to 0.058 mol CO
2
/mol quantum, which
was similar to the range from 0.037 to 0.069
mol CO
2
/mol quantum estimated in Begonia
semperflorens-cultorum Hort. (Nemali and
van Iersel, 2004). Plants grown under PPFD
of 285 and 350 mmolm
–2
s
–1
and treated by
paclobutrazol at 150 mgL
–1
had lower quan-
tum yields than those grown under the PPFD
of 350 mmolm
–2
s
–1
without paclobutrazol
treatment or those grown under 550 mmol
m
–2
s
–1
irrespective of paclobutrazol treat-
ment (Table 2). Correspondingly, A
max
of
Table 2. Maximum net photosynthesis rate (A
max
), quantum yield (A
qe
), light compensation point (LCP), and light saturation point (LSP) of Pachira aquatica
plants grown under different light intensities and treated with different rates of paclobutrazol.
Light intensity
(mmolm
–2
s
–1
)
Paclobutrazol concn
(mgL
–1
)A
max
(mmol CO
2
/m
–2
s
–1
)A
qe
(mol CO
2
/mol quantum) LCP (mmolm
–2
s
–1
) LSP (mmolm
–2
s
–1
)
285 0 3.3 abc
z
0.042 ab 9.0 b 256.2 ab
285 50 3.1 abc 0.041 ab 9.0 b 226.4 ab
285 150 2.5 c 0.033 b 8.0 b 213.5 b
350 0 4.2 ab 0.054 a 11.0 ab 242.1 ab
350 50 3.1 abc 0.045 ab 9.0 b 219.3 ab
350 150 2.6 c 0.038 b 8.0 b 217.6 ab
550 0 4.7 a 0.058 a 16.0 a 259.3 a
550 50 4.4 ab 0.057 a 11.0 ab 249.4 ab
550 150 3.9 ab 0.054 a 10.0 b 218.5 ab
Significance
y
Light * * * *
Paclobutrazol * NS NS NS
Interaction NS NS NS NS
z
Means within column followed by different letters are significantly different by Duncan’s new multiple range test at P= 0.05.
y
NS indicates nonsignificant; *significant at P= 0.05 (n = 9).
Fig. 1. The leaf transverse sections of Pachira aquatica grown under daily maximum photosynthetic
photon flux densities (PPFD) of 285 mmolm
–2
s
–1
(A) and 550 mmolm
–2
s
–1
(B). More elongated
palisade mesophyll cells occurred in leaves of plants grown under PPFD of 550 mmolm
–2
s
–1
(B)
compared with the leaves produced under 285 mmolm
–2
s
–1
(A). The palisade cells were vertically
aligned more tightly in the leaves of plants grown under 550 mmolm
–2
s
–1
than in the leaves of plants
grown under 285 mmolm
–2
s
–1
. Ad = adaxial epidermal cells; Pa = palisade parenchyma; Sp = spongy
parenchyma; Ab = abaxial epidermal cuticle cells. Bar = 0.1 mm.
Fig. 2. Photosynthetic -light response curves of Pachira aquatica plants one year after growing in a shaded
greenhouse under three daily maximum photosynthetic photon flux densities of 550 (o), 350 (D), and
285 (h)mmolm
–2
s
–1
with a foliar spray of paclobutrazol at concentrations of 0 (A), 50 (B), and 150
(C)mgL
–1
.
HORTSCIENCE VOL. 44(5) AUGUST 2009 1293
those plants with the reduced quantum yield
significantly decreased. However, conflicting
results exist regarding paclobutrazol effects
on photosynthesis. Vu and Yelenosky (1992)
reported that net photosynthesis of Citrus
sinensis (L.) Osbeck was reduced by paclobu-
trazol application, whereas Jaleel et al. (2007)
reported that photosynthesis of Catharanthus
roseus (L.) G. Don. was enhanced by paclo-
butrazol. The results from the present study
were in agreement with those reported by Vu
and Yelenosky (1992). The reduced net pho-
tosynthetic rate in P.aquatica was correlated
with the reduction in the quantum yield (Table
2). The quantum yield of CO
2
assimilation has
been widely used for evaluating the efficiency
of photosynthesis at low PPFD (Ehleringer
and Bjorkman, 1977).
Light compensation points of P.aquatica
grown under PPFD of 285 mmolm
–2
s
–1
ranged from 8.0 to 9.0 mmolm
–2
s
–1
, which
was not significantly affected by paclobutra-
zol application (Table 2). However, light
compensation points of plants grown under
350 and 550 mmolm
–2
s
–1
decreased from
11.0 to 8.0 and from 16.0 to 10.0 mmolm
–2
s
–1
,
respectively. The light compensation point
reduction appeared to relate to the reduction
of quantum yield and maximum net photo-
synthetic rate (Table 2).
Leaf anatomical differences. Microscopic
observations showed more elongated pali-
sade mesophyll cells in leaves of P.aquatica
grown under PPFD of 550 mmolm
–2
s
–1
(Fig.
1B) compared with the leaves produced
under 285 mmolm
–2
s
–1
(Fig. 1A) or under
350 mmolm
–2
s
–1
regardless of paclobutrazol
application. The elongation of palisade cells
resulted in slightly thicker leaves when plants
were grown under 550 mmolm
–2
s
–1
. The
palisade cells in the leaves of plants grown
under 550 mmolm
–2
s
–1
were vertically and
more tightly aligned compared with the
loosely arrayed palisade cells in the leaves
of plants grown under 285 mmolm
–2
s
–1
. The
tight alignment resulted in the reduction of
intercellular spaces with a larger number of
palisade cells per unit area (Fig. 1). Thus, net
photosynthetic rates of plants grown under
PPFD of 550 mmolm
–2
s
–1
were higher than
those grown under the low PPFD. The
palisade cell orientation was similar to that
observed in F. benjamina (Fails et al., 1982)
in which palisade cells were tightly aligned
along radial walls in leaves of plants grown
under high PPFD compared with a loose
alignment in leaves of plants grown under
low PPFD. However, unlike F. benjamina in
which there were multiple layers of palisade
cells, leaves of P.aquatica had only one layer
of palisade cells.
Effects on interior performance. Plant
growth after placement indoors for 6 months
depended on treatment. Canopy height
increase ranged from 0.2% to 6.5% for plants
treated with paclobutrazol and 8.0% to 11.1%
for those without paclobutrazol treatment
(Table 3). Canopy width increase varied from
0.1% to 6.8% regardless of treatment, but
such an increase was not significant. The
results showed that residual effects of paclo-
butrazol remained in plants for 16 months.
Karaguzel and Ortacesme (2002) reported
that internode lengths of Bougainvillea gla-
bra Choisy ‘Sanderiana’ treated with a foliar
spray of paclobutrazol could reach the inter-
node lengths of control plants in only 120 d.
The prolonged effect may indicate that P.
aquatica is more sensitive to paclobutrazol
than B.glabra because plant species differ-
ences in paclobutrazol sensitivity have been
widely documented (Barrett et al., 1994;
Wang and Blessington, 1990).
There was little change in mean internode
length and canopy height of plants treated by
paclobutrazol at 150 mgL
–1
irrespective of
production light levels. Canopy heights,
mean internode lengths, and the percentage
of canopy height increases were also signif-
icantly decreased by paclobutrazol treatment
at 50 mgL
–1
. Leaflet drop occurred 3 weeks
after placement indoors. Production PPFD
played a more important role in preventing
leaflet drop than paclobutrazol treatment.
Regardless of paclobutrazol treatment, the
number of leaflets dropped ranged from 10
to 23 for plants produced under 550
mmolm
–2
s
–1
compared with one to five and
six to 12 for those produced under 285 and
350 mmolm
–2
s
–1
, respectively. The reduced
leaflet drop is probably because the plants
grown under low PPFD had low light com-
pensation points, thus allowing them to better
and more quickly adapt to interior low light
conditions. Similar results were also reported
in Chamaedorea elegans Mart. (Reyes et al.,
1996), F. benjamina (Chen et al., 2005b;
Fonteno and McWilliams, 1978; Pass and
Hartley, 1979), Hedera helix L. (Yeh and
Hsu, 2004), and Leea coccina L. and Leea
rubra L. (Sarracino et al., 1992).
Paclobutrazol treatment also reduced
leaflet drop; such reduction was more pro-
nounced for plants produced under PPFD of
550 mmolm
–2
s
–1
than those produced under
285 mmolm
–2
s
–1
. Reduced leaf drop was
reported in F. benjamina during a simu-
lated shipping and interiorscape when plants
were treated with ancymidol (Peterson and
Blessington, 1982). The interior performance
of F. benjamina,Radermachera sincica
(Hance) Hemsl., and Epipremnum aureum
(Linden & Andre) Bunt. was improved by
paclobutrazol application (Barrett and Nell,
1983; Poole and Conover, 1992). However,
there has been no report on paclobutrazol
application in the reduction of leaf drop. The
leaf drop reduction in P.aquatica could also
be attributed to the fact that paclobutrazol
treatment decreased the light compensation
points of plants grown under 550 mmol
m
–2
s
–1
(Table 2).
In conclusion, P.aquatica responded to
decreasing production PPFD and paclobutra-
zol application rates by reducing net photosyn-
thetic rates, lowering light compensation
points, and reducing internode lengths and
canopy heights and widths. Plants with the
Table 3. Canopy heights and widths, percentage of canopy height and width increase, and leaf drop of Pachira aquatica plants after placing in interior conditions
for 6 months.
z
Light intensity
(mmolm
–2
s
–1
)
Paclobutrazol concn
(mgL
–1
)
Six months after placement indoors Mean internode
length (cm)
x
Percentage of increase
y
Leaflet
drop (no.)Canopy ht (cm) Canopy width (cm) Canopy ht Canopy width
285 0 90.5 a
w
92.8 a 11.0 a 11.1 a 0.1 5 c
285 50 63.7 b 88.8 ab 1.3 b 5.5 b 3.1 4 c
285 150 45.5 c 61.9 c 0.9 b 0.0 d 2.3 1 c
350 0 88.4 a 90.7 ab 11.3 a 8.6 a 0.1 12 bc
350 50 59.2 b 82.0 abc 0.9 b 6.5 b 5.4 8 c
350 150 45.4 c 70.9 c 0.9 b 0.0 d 6.8 6 c
550 0 89.4 a 91.1 ab 12.1a 8.0 a 4.2 23 a
550 50 62.4 b 86.8 ab 1.2 b 5.1 b 4.8 20 b
550 150 46.8 c 58.4 bc 0.9 b 3.1 c 1.2 10 c
Significance
v
Light NS NS NS NS NS *
Paclobutrazol ** ** ** ** NS *
Interaction NS NS NS NS NS *
z
Plants were placed indoors for 6 months under a photosynthetic photon flux density (PPFD)of18mmolm
–2
s
–1
. The plants were produced in a shaded greenhouse
under three PPFD for 1 year and treated by a one-time foliar application of three rates of paclobutrazol 2 months after potting.
y
The percentage of canopy height or width increase was calculated as follows: (height or width at the end of indoor evaluation – height or width at the end of
production)/height or width at the end of production.
x
The mean internode length was the stem height divided by the number of nodes.
w
Means within column followed by different letters are significantly different by Duncan’s new multiple range test at P= 0.05.
v
NS indicates nonsignificant; **significant at P= 0.01 and *significant at P= 0.05 (n = 5).
1294 HORTSCIENCE VOL. 44(5) AUGUST 2009
compact growth form grew slowly and drop-
ped few leaflets, thus maintaining their aes-
thetic appearance after placement indoors for 6
months. Based on the results presented in this
study, it is suggested that production of P.
aquatica under a PPFD range between 285 and
350 mmolm
–2
s
–1
with one-time foliar spraying
of paclobutrazol at a concentration between 50
and 150 mgL
–1
after canopy establishment can
result in plants with a compact appearance and
prolonged interior performance.
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HORTSCIENCE VOL. 44(5) AUGUST 2009 1295
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